Shoulder joint is one of the most mobile joint in the human body having the maximum mobility. It is a type of ball and socket joint where the ball is formed by the humeral head and the socket by the glenoid along with its labrum. The glenoid is very small compared to the humeral head and needs the  soft labrum to contain the humerus in its socket. The small socket along with the soft labrum results in the great arc of movement.  The muscles around the shoulder add to the stability of the joint. Shoulder joint replacement is done for the following cases:

• Osteo Arthritis: It is the age related wear and tear of the articular surfaces that results in debilitating pain and restriction of movement of the affected joint. The articular cartilage which acts as a cusion between the two bony surfaces gets eroded resulting in rubbing of the bones together causing pain and joint destruction.
• Rheumatoid Arthritis : inflammatory condition of the synovial membrane causing severe joint destruction. It affects multiple joints.
• Avascular necrosis: Disruption of the blood supply to the bone causes necrosis ultimately resulting in joint destruction .
• Fractures : severely comminuted fracture of the proximal humerus result in difficult fixation resulting in loss of normal anatomy. Furthermore there is a high chance of loss of vascularity to the humeral head and hence in some cases, shoulder arthroplasty maybe recommended.

Types

1. Shoulder resurfacing

Shoulder resurfacing is a hemiarthroplasty in which only a part of the joint is replaced. As the name suggests, only the involved joint surface is replaced and the rest of the bones and joint remain intact. This is done only when the humeral head is involved. The glenoid cartilage needs to be intact and the rotator cuff muscles need to be intact for a successful surgery.

2. Shoulder arthroplasty

Shoulder arthroplasty is done for the above mentioned causes where the proximal surface of the humerus is replaced with a metal prosthesis. The rotator cuff muscle attached over the prximal humerus are reattached around the metal prosthesis using bone pieces from the excised bone pieces. The rotator cuff muscles need to be intact for a successful surgery.

3. Reverse shoulder arthroplasty

As the name suggests the shoulder joint is reversed! The glenoid becomes the ball and the humerus becomes the socket and hence the name ‘Reverse’ Shoulder. This type of surgery is done for patients with a destroyed joint along with torn or atrophied rotator cuff muscles. This design of the shoulder uses the power of the deltoid for shoulder movement and thus can be used for patients with rotator cuff disesases.

Post operative rehabilitation

As the muscles are all detached and reattached during the surgery, movement of the joint are started after the healing of the muscles. Pendulum exercises may be started after the surgery but abduction exercises are started only after 6 weeks. The final range of motion achieved by the patient depends upon the strength and function of the rotator cuff muscles. The patient will be relieved of the pain and the motion at the joint is increased but is still less compared to the normal joint.

 Expectations

Shoulder replacement surgery primarily aims at pain relief. Secondary aim of the procedure is achieve a good range of motion of the joint. The range of motion of the joint is depended mainly on the condition of the muscles around the joint. Patients with arthritis usually have poor range of motion due to disuse atrophy of the muscles over the years as the patient has not been moving the joint due to pain. Rotator cuff muscles need to be intact for a successful surgery and if not intact, a reverse shoulder arthroplasty is preferred.